Last decade has seen a resurge in renewable resource based polymeric materials. Among the various renewable resources, sugars and plant oils provide direct entry to chemical modification and functionalization. Hence, sugars and plant oils are the most competitive candidates for further utilization in platform chemicals and polymerization. There are polymers that are renewable resource based, but do not degrade. Secondly, there are polymers which come from fossil fuels but degrade. However, there are hardly few, which come from renewables and are also degradable. Thus, degradability is another material requirement for clean and sustainable future.
Renewable resource based polyacetals seems to meet these two criteria. It has been found that oil based polyacetals undergo hydrolytic degradation. Despite this progress, sugar based acetal monomers have remain elusive and unexplored.
Isohexides derived from monomeric unit of carbohydrate which are non-toxic, have excellent structural rigidity are a promising surrogate for fossil fuel-derived diols. The exo-endo configuration of the hydroxyl groups further boosts the versatility of isosorbide leading to several applications in renewable chemicals, solvents, fuel, as chiral auxiliary.
Isohexide-acetals are now looked upon as decisive next generation of sustainable materials that would meet both the criteria viz. renewability and degradability thus contributing to green chemistry.
Furthermore, synthesis of acetal polymer and copolymer is challenging since polyacetals are sensitive to acid catalyzed hydrolytic cleavage.
In an Article titled, “Acetal metathesis polymerization (AMP): A method for Synthesizing biorenewable polyacetals” by Alexander G. Pemba, Jeniree A. Flores and Stephen A. Miller in Green Chem., 2013, 15, 325-329 reports the synthesis of Polyalkylene acetals from simple bio-derived diols and diethoxymethane via a novel technique involving interchange of acetal functional groups. This Acetal Metathesis Polymerization (AMP) method provides a route to polyacetals that are designed to degrade under abiotic conditions via simple acid catalyzed hydrolysis.
Publication no. WO 2012/129070 A2 discloses a method of preparing a polyacetal comprising polymerization of a mixture comprising a plurality of at least one bis-acetal monomer in the presence of an acid catalyst that promotes the metathesis of the acetal units. The bis acetal can be formed from an acid catalysed exchange between a mono acetal monomers with a diol. It is further mentioned that formation of the bis-acetal and the polyacetal can be carried out simultaneously. Moreover, WO'070 mentions the use of C5 to C10 linear chain diols for preparation of acetals. Furthermore, the copolymers are obtained by reaction of long chain diols with diacetals.
In pursuit to present a new class of renewable and degradable polymers that can meet both the criteria of sustainable materials, the present invention is directed to provide sugar based monomers and polymers which are stable yet degradable under mild acidic conditions.